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    <title>Document</title>
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<body>
    <div>请输入一个字符串</div>
    <input id="parent" type="text">
    <div>请输入一个子串</div>
    <input type="text" id="son">
    <button onclick="main()">提交</button>
    <div>子串出现了多少次</div>
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